ant are well understood, but they require too much knowledge of
chemistry to be easily comprehended by the young learner, and it is not
absolutely essential that they should be understood by the scholar who
is merely learning the _elements_ of the science.

It is sufficient to say that the food taken up by the plant undergoes
such changes as are required for its growth; as in animals, where the
food taken into the stomach, is digested, and formed into bone, muscle,
fat, hair, etc., so in the plant the nutritive portions of the sap are
resolved into wood, bark, grain, or some other necessary part.

The results of these changes are of the greatest importance in
agriculture, and no person can call himself a _practical farmer_ who
does not thoroughly understand them.

CHAPTER VI.

PROXIMATE DIVISION OF PLANTS, ETC.

We have hitherto examined what is called the _ultimate_ division of
plants. That is, we have looked at each one of the elements separately,
and considered its use in vegetable growth.

[Of what do wood, starch and the other vegetable compounds
chiefly consist?

Are their small ashy parts important?

What are these compounds called?

Into how many classes may proximate principles be divided?

Of what do the first class consist? The second?

What vegetable compounds do the first class comprise?]

We will now examine another division of plants, called their _proximate
division_. We know that plants consist of various substances, such as
wood, gum, starch, oil, etc., and on examination we shall discover that
these substances are composed of the various _organic_ and _inorganic_
ingredients described in the preceding chapters. They are made up almost
entirely of _organic_ matter, but their ashy parts, though very small,
are (as we shall soon see) sometimes of great importance.

These compounds are called _proximate principles_,[G] or _vegetable
proximates_. They may be divided into two classes.

The first class are composed of _carbon_, _hydrogen_, and _oxygen_.

The second class contain the same substances and _nitrogen_.

[Are these substances of about the same composition?

Can they be artificially changed from one to another?

Give an instance of this.

Is the ease with which these changes take place important?

From what may the first class of proximates be formed?]

The first class (those compounds not containing nitrogen) comprise the
wood, starch, gum, sugar, and fatty matter